feat(providers): add support for custom vendors (#74)

* feat(providers): add support for custom vendors

Signed-off-by: Aaron Pham <contact@aarnphm.xyz>

* fix: override configuration not setup

Signed-off-by: Aaron Pham <contact@aarnphm.xyz>

---------

Signed-off-by: Aaron Pham <contact@aarnphm.xyz>

lua/avante/config.lua

@@ -6,7 +6,7 @@ local M = {}
 
 ---@class avante.Config
 M.defaults = {
-  ---@alias Provider "openai" | "claude" | "azure" | "deepseek" | "groq"
+  ---@alias Provider "openai" | "claude" | "azure" | "deepseek" | "groq" | [string]
   provider = "claude", -- "claude" or "openai" or "azure" or "deepseek" or "groq"
   openai = {
     endpoint = "https://api.openai.com",
@@ -39,6 +39,10 @@ M.defaults = {
     temperature = 0,
     max_tokens = 4096,
   },
+  --- To add support for custom provider, follow the format below
+  --- See https://github.com/yetone/avante.nvim/README.md#custom-providers for more details
+  ---@type table<string, AvanteProvider>
+  vendors = {},
   behaviour = {
     auto_apply_diff_after_generation = false, -- Whether to automatically apply diff after LLM response.
   },
@@ -100,6 +104,11 @@ function M.setup(opts)
   )
 end
 
+---@param opts? avante.Config
+function M.override(opts)
+  M.options = vim.tbl_deep_extend("force", M.options, opts or {})
+end
+
 M = setmetatable(M, {
   __index = function(_, k)
     if M.options[k] then